The present invention relates to a device and a method of adjusting a variable boosting factor of a controlled, independently activatable brake power booster which boosts an input force and converts it into a deceleration of an automotive vehicle.
The boosting factor i, i.e. the ratio between input force and output force, is invariably adjusted in conventional brake power boosters. This factor is fixed in the development of the brake power booster within limits predefined by construction. The output force of the brake power booster acts upon a master brake cylinder and thereby generates a braking pressure which is virtually proportional to the output force, thus providing deceleration of the automotive vehicle.
A disadvantage of brake systems equipped with a brake power booster of this type is that the ratio between pedal force and automotive vehicle deceleration is not constant. The ratio is subject to variable parameters such as vehicle mass, coefficients of friction of linings, and rates of hydraulic efficiency. The driver must acclimate to these variations in the braking behavior. To relieve the driver, it is desirable to adapt the brake system so that a constant ratio between the pedal force of the driver and the vehicle deceleration can be adjusted. This necessitates a brake power booster with a variable boosting factor which permits compensating the influence of variable parameters also during operation.
Further, independently activatable brake power boosters are disclosed in the art, for example, in German patent application No. 43 24 688.5. This publication discloses a vacuum brake power booster wherein a third sealing seat on the poppet valve renders it possible to effect an independent assist braking operation irrespective of the activation by the driver.